According to my humble opinion, here are other reasons for some of the plagues:

1. **Blood:**Because the Egyptians so severely subjugated the Israelites, their blood turned to water, so God turned their water into blood.

2. Frogs: The Egyptians would complain and shout at the Israelites, “Work, work, you lazy ones. God to your labors,” therefore, he brought frogs upon them to scream and shout, as the Midrash says: “the sound of the frogs was so loud in Egypt, that it seemed to enter their bodies and felt like it was coming from within them.”

3. Lice: Because the Egyptian task masters made the Israelites worked all the time, they had no time to change their clothes and to clean their garments or comb their hair so that soon everything was covered with lice. Therefore, God brought lice upon the Egyptians, measure for measure.

4. Wild beasts: because they attacked the Israelites in mobs, so God brought mobs of beasts, measure for measure.

5. Boils: The Egyptians used to bathe in hot water. If the water was too hot they would force the Israelite slaves to go into the water to cool it off, thus causing abrasions on their skin. Measure for measure, God afflicted the skin of the Egyptians.

Darkness: Why did the Holy cause a plague of darkness? Nothing is hidden from the Holy One, even that which is deep in our hearts and minds. There were those among the Israelites who were released from bondage by the Egyptians were given great honor and wealth. They did not wish to leave Egypt. The Holy One said: "If I bring a plague upon them publically and they die, the Egyptians will say, 'Just as God has attacked us so he is attacking your people.'” Therefore God brought darkness upon the Egyptians for three days so that the Israelites could bury their dead (who were struck down by God) , and the Egyptians would not see this. Also during the three days of darkness, God caused the Egyptians to look more favorably upon the Israelites, and they gave them whatever they asked for. The Israelites were able to enter the homes of the Egyptians and see where their silver, gold and fine garments were hidden. If the Egyptians said we have nothing to give you, the Israelites would respond, “Isn’t such and such a thing in such and such a place?” At that time the Egyptians reasoned: “If the Israelites wanted to lie to us they could have just taken what they wanted during the days of darkness, since they have already seen the things we have. Since they did not take anything without our knowledge, we will freely give these things to them.” Thus they fulfilled the prophecy given to Abraham, “Afterwards they shall leave with great wealth.” That is why the Torah does not say there was light in the land of Goshen but in their dwelling places. Wherever an Israelite dwelled he had light.

The death of the first born: Because Israel was called God’s first born, as it says, “My first born son, Israel.” Jacob acquired the birthright so that he could serve God. God said: “Let My children go that they may serve me. If you refuse to let my first born go to serve Me, I will prevent your first born from serving you; I will kill all of them!”